Abundance, distribution, and isotopic composition of particulate black carbon in the northern Gulf of Mexico

Abstract

There exists increasing evidence supporting the important role of black carbon in global carbon cycles. Particulate black carbon (PBC) is allochthonous and has distinct reactivities compared to the bulk particulate organic carbon (tot-POC) in marine environments. However, the abundance, geochemical behavior of PBC and its importance in oceanic carbon budget remain poorly understood. Here we report the abundance, distribution, and stable isotopic signatures of BC derived from the chemo-thermal oxidation (CTO-375) method (BC CTO) in the Gulf of Mexico. Our results show that BC CTO abundance decreased from shelf to basin, and more than a half of riverine BC CTO could be removed over the shelf. Moreover, BC CTO is much more refractory compared to the tot-POC and has δ 13 C values lower than those of BC-excluded POC. These results highlight the significance of PBC in marine carbon cycles and potentially suggest the need for a new end-member term in quantifying POC sources in the ocean. Key Points BC could result in an overestimate of autochthonous POC in the ocean13C abundance of soot BC is up to 12‰ lower than BC-excluded POC>50% of the riverine soot BC is removed on the shelf